Paramilitary security force officers stand under a portrait of the late Chinese leader Mao Zedong outside the Forbidden City on June 2 at Tiananmen Square in Beijing. Twenty-five years ago on June 4, 1989, Chinese troops staged a brutal crackdown on pro-democracy protesters after the government ordered the square cleared. Kevin Frayer, Getty Images

Thousands of pro-democracy protesters gather around the Goddess of Democracy statue as they fill Tiananmen Square on June 2, 1989. Hundreds of demonstrators were killed when Chinese troops cleared the square on June 3-4. Catherine Henriette, AFP/Getty Images

A photograph taken on June 5, 1989, top, shows a lone Chinese man blocking a line of tanks heading east on Changan Boulevard near Tiananmen Square. A May 27 photograph of the same spot shows a convoy of cars crossing the intersection. Jeff Widener, top, and Helene Franchineau, AP

A May 28, 1989, photograph shows students resting at Tiananmen Square. Twenty-five years years later, on May 31, Chinese tourists use their smartphones and digital cameras to take souvenir photos as slogans are displayed on electric screens. Jeff Widener, top, and Alexander F. Yuan, AP

People's Liberation Army troops and armored vehicles guard Tiananmen Gate on June 10, 1989. On May 28 Chinese paramilitary police clear tourists from the area for a flag-lowering ceremony on Tiananmen Square. Sadayuki Mikami, top, and Alexander F. Yu, AP

A May 26, 1989, photograph, top, shows a sanitation worker cleaning Tiananmen Square. On May 22 a sanitation worker, who is also a member of a group of civilian security informers, watches tourists while patrolling on her electric scooter. Jeff Widener, top, and Alexander F. Yuan, AP

In this combination of photos, a May 16, 1989, file photo, top, shows medics rushing a Beijing University student from Tiananmen Square after he collapsed on the third day of a hunger strike on May 16, 1989. In the bottom photo, on May 16, 2014, a group of high school students prepare to board a bus after they performed a ceremony around the Monument to the People's Heroes on Tiananmen Square. Sadayuki Mikami, top, and Alexander F. Yu, AP

People pass armored vehicles parked in front of Tiananmen Gate on June 13, 1989. A security guard watches an empty bicycle lane in a cordoned off area in front of Tiananmen Gate on May 24. Sadayuki Mikami, Alexander F. Yu AP

A student leader reads a list of demands during an April 18, 1989, sit-in at the Great Hall of the People in Beijing. A May 29 photograph shows People's Liberation Army soldiers marching to their positions before an honor guard performance. Kathy Wilhelm, top, and Alexander F. Yuan, AP

The bodies of dead civilians lie among mangled bicycles near Tiananmen Square on June 4, 1989, after government troops staged a bloody crackdown on pro-democracy protesters. AP